What is the call handling limit for the unlimited version of the HAAst? Does it depend only on Hardware and Asterisk limitations? We plan to install a pair of Asterisk servers with 400 simultaneous calls. Is it possible to use HAAst with them?

The unlimited edition of HAAst does not impose any limit on number of simultaneous calls. From a practical standpoint HAAst is limited only by the capacity of your hardware, and the design of Asterisk.

If you are at the point of sizing hardware for purchase, we recommend adding 5% to CPU capacity, and 500MB to memory capacity for HAAst, above what is demanded by Asterisk. (Which in the overall scale of these systems is negligible).